How much preamp will improve

Andy2, the HT pass through is simply one button, even I can do it!

I think you can have the best of two worlds by having a preamp with a HT bypass. It would be a bit cumbersome to operate but I don't mind (having no wife yet :-)).

i'm using a HT-oriented pre/pro (rotel rsx-1055) - it's actually a reciever, but for 2ch i'm using the main outs to separate amplification - and i can tell you from having tried several 2ch outboard preamps (in place of the rotel) that there is A LOT of room for improvement there. i've used tube based pieces such as the Eastern Electric, and an old-school PAS-3 (non-X) and found they changed the character of the entire system drastically. i've also used other HT pre-amp only (outboard processors) and found things were different.

note, i said different. not always better. simply put, you're going to need some AMAZING (read: $$$) interconnects in order to overcome the separation of the two pieces. put another way: moving the processor out of the same box of the pre might solve a few things like power supply, noise, whatever, but has the potential to cause a LOT of headache / nightmares / costs.

for HT, i'd say either get a better integrated pre/proc. and amp, rather than spend money on separeate processors and preamps (the only reason i'd suggest that is for upgradability re: different formats in the future). for 2ch / music, i'd say, separate them to your heart's content: lets put it this way, you can spend the $$ on 2 really nice ICs vs 8 for 7.1 :)

I dump my whole HT setup because I enjoy listen to music more than getting shaked by the pounding from the movies.
I used to have sony 9000ES digital preamp with Bryston 9 BST. The music never as good in HT preamp. The first preamp I jump on was Audio Research SP-11 MKII. Even to this day, SP-11 MKII is still one of the best preamp out there. Another recommendation is Counterpoint SA-5000. This is the bargain in preamp. Very nice and sweet sound like no other preamp and yet it is very transparent and not muddy.

Kr4: It's only a suspicion or a guess from my part. It usually sounds fine when I am using the Nad541. When I am using the Cary303, I feel like the 303 stresses the system a bit. And the only thing I can think of is my preamp stage is not up to the task.

What's wrong with the AR? What do you think it is doing to the sound?

I do not know about your processor, but I have used two fairly good preamps with my older Lexicon HT processor, since I am more into the two channel for music. The Adcom GFP750 (mine had black gate cap upgrades) sounded quite good for what they cost, as well as having a passive option. The best I have used is my Muse Model Three Signature, which sounds great. It has individual gain setting for 5 inputs, balanced and rca inputs and ouputs (fully balanced design), and is considered a "reference" product by Muse. I have stumbled on two of these and currently have one for sale here, if you are interested. IMO much better than the Adcom. Other mfg's also make good preamps with HT pass through, such as McCormack, BAT and others. If you don't want to spend much, start with the Adcom for about $650-$750 since you can try it and sell it for about what you pay, if you don't like it, or to upgrade.